Description Usage Arguments Details Value Author(s) References See Also Examples
View source: R/MaskAlignment.R
Automatically masks poorly aligned regions of an alignment based on sequence conservation and gap frequency.
1 2 3 4 5 6 7 8 | MaskAlignment(myXStringSet,
type = "sequences",
windowSize = 5,
threshold = 1,
maxFractionGaps = 0.2,
includeTerminalGaps = FALSE,
correction = FALSE,
showPlot = FALSE)
|
myXStringSet |
An |
type |
Character string indicating the type of result desired. This should be (an abbreviation of) one of |
windowSize |
Integer value specifying the size of the region to the left and right of the center-point to use in calculating the moving average. |
threshold |
Numeric giving the average entropy in bits below which a region is masked. |
maxFractionGaps |
Numeric specifying the maximum faction of gaps in an alignment column to be masked. |
includeTerminalGaps |
Logical specifying whether or not to include terminal gaps ("." or "-" characters on each end of the sequences) into the calculation of gap fraction. |
correction |
Logical indicating whether to apply a small-sample size correction to columns with few letters (Yu et al., 2015). |
showPlot |
Logical specifying whether or not to show a plot of the positions that were kept or masked. |
Poorly aligned regions of a multiple sequence alignment may lead to incorrect results in downstream analyses. One method to mitigate their effects is to mask columns of the alignment that may be poorly aligned, such as highly-variable regions or regions with many insertions and deletions (gaps).
Highly variable regions are detected by their signature of having a low information content. Here, information content is defined by the relative entropy of a column in the alignment (Yu et al., 2015), which is higher for conserved columns. The relative entropy is based on the background distribution of letter-frequencies in the alignment.
A moving average of windowSize
nucleotides to the left and right of the center-point is applied to smooth noise in the information content signal along the sequence. Regions dropping below threshold
bits or more than maxFractionGaps
are masked.
If type
is "sequences"
then a MultipleAlignment
object of the input type with masked columns where the input criteria are met. Otherwise, if type
is "ranges"
then an IRanges
object giving the start and end positions of the masked columns. Else (type
is "values"
) a data.frame
containing one row per site in the alignment and three columns of information:
"entropy" |
The entropy score of each column, in units of bits. |
"gaps" |
For each column, the fraction of gap characters ("-" or "."). |
"mask" |
A logical vector indicating whether or not the column met the criteria for masking. |
Erik Wright eswright@pitt.edu
Yu, Y.-K., et al. (2015). Log-odds sequence logos. Bioinformatics, 31(3), 324-331. http://doi.org/10.1093/bioinformatics/btu634
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | fas <- system.file("extdata", "Streptomyces_ITS_aligned.fas", package="DECIPHER")
dna <- readDNAStringSet(fas)
masked_dna <- MaskAlignment(dna, showPlot=TRUE)
# display only unmasked nucleotides for use in downstream analyses
not_masked <- as(masked_dna, "DNAStringSet")
BrowseSeqs(not_masked)
# display only masked nucleotides that are covered by the mask
masked <- masked_dna
colmask(masked, append="replace", invert=TRUE) <- colmask(masked)
masked <- as(masked, "DNAStringSet")
BrowseSeqs(masked)
# display the complete DNA sequence set including the mask
masks <- lapply(width(colmask(masked_dna)), rep, x="+")
masks <- unlist(lapply(masks, paste, collapse=""))
masked_dna <- replaceAt(dna, at=IRanges(colmask(masked_dna)), value=masks)
BrowseSeqs(masked_dna)
# get the start and end ranges of masked columns
ranges <- MaskAlignment(dna, type="ranges")
ranges
replaceAt(dna, ranges) # remove the masked columns
# obtain the entropy scores of each column
values <- MaskAlignment(dna, type="values")
head(values)
|
Loading required package: Biostrings
Loading required package: BiocGenerics
Loading required package: parallel
Attaching package: ‘BiocGenerics’
The following objects are masked from ‘package:parallel’:
clusterApply, clusterApplyLB, clusterCall, clusterEvalQ,
clusterExport, clusterMap, parApply, parCapply, parLapply,
parLapplyLB, parRapply, parSapply, parSapplyLB
The following objects are masked from ‘package:stats’:
IQR, mad, sd, var, xtabs
The following objects are masked from ‘package:base’:
anyDuplicated, append, as.data.frame, basename, cbind, colnames,
dirname, do.call, duplicated, eval, evalq, Filter, Find, get, grep,
grepl, intersect, is.unsorted, lapply, Map, mapply, match, mget,
order, paste, pmax, pmax.int, pmin, pmin.int, Position, rank,
rbind, Reduce, rownames, sapply, setdiff, sort, table, tapply,
union, unique, unsplit, which.max, which.min
Loading required package: S4Vectors
Loading required package: stats4
Attaching package: ‘S4Vectors’
The following object is masked from ‘package:base’:
expand.grid
Loading required package: IRanges
Loading required package: XVector
Attaching package: ‘Biostrings’
The following object is masked from ‘package:base’:
strsplit
Loading required package: RSQLite
IRanges object with 13 ranges and 0 metadata columns:
start end width
<integer> <integer> <integer>
[1] 19 19 1
[2] 170 213 44
[3] 230 230 1
[4] 235 235 1
[5] 267 286 20
... ... ... ...
[9] 378 394 17
[10] 399 406 8
[11] 418 418 1
[12] 420 442 23
[13] 495 496 2
DNAStringSet object of length 88:
width seq names
[1] 473 TGTACACACCGCCCGTCACGTCA...GGGGTTTCCGAATGGGGAAACC supercont3.1 of S...
[2] 473 NNNNCACACCGCCCGTCACGTCA...GGGGTTTCCGAATGGGGAAACC supercont3.1 of S...
[3] 473 TGTACACACCGCCCGTCACGTCA...GGGGTTTCCGAATGGGGAAACC supercont1.1 of S...
[4] 473 CGTACACACCGCCCGTCACGTCA...GGGGTTTCCGAATGGGGAAACC supercont1.1 of S...
[5] 473 TGTACACACCGCCCGTCACGTCA...GGGGTTTCCGAATGGGGAAACC supercont1.1 of S...
... ... ...
[84] 473 TGTACACACCGCCCGTCACGTCA...GGGGTTTCCGAATGGGGAAACC gi|297189896|ref|...
[85] 473 TGTACACACCGCCCGTCACGTCA...GGGGTGTCCGAATGGGGAAACC gi|224581106|ref|...
[86] 473 TGTACACACCGCCCGTCACGTCA...GGGGTGTCCGAATGGGGAAACC gi|224581106|ref|...
[87] 473 TGTACACACCGCCCGTCACGTCA...GGGGTGTCCGAATGGGGAAACC gi|224581106|ref|...
[88] 473 TGTACACACCGCCCGTCACGTCA...GGGGTTTCCGAATGGGGAAACC gi|224581108|ref|...
entropy gaps mask
1 1.895882 0 FALSE
2 1.260362 0 FALSE
3 1.964568 0 FALSE
4 2.087429 0 FALSE
5 1.889936 0 FALSE
6 2.211969 0 FALSE
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